Circuit interrupter



Feb. 24, 1959 M. P. WHITE CIRCUIT INTERRUPTER 3 Sheets-Sheet 1 Filed March 50', 1956 Fig.3.

Filed March 50, 1956 M. P. WHITE CIRCUIT INTERRUPTER 3 Sheets-Sheet 2 United States Patent CIRCUIT INTERRUPTER Marshall P. White, Buffalo, N. Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 30, 1956, Serial No. 575,036 7 Claims. (Cl. 200-147) This invention relates generally to circuit interrupting devices and more particularly to such a device having an improved arc extinguishing arrangement.

In general, a circuit interrupting device may comprise a contact assembly involving a stationary and movable contact together with some means for actuating the movable contact between positions engaging and disengaging the stationary contact. The actuating means may be of the form of an electromagnetic device involving a core and a coil assembly disposed in operable flux linking relationship with an armature member mounted on the movable contact structure. To aid in extinguishing the are which is struck when the movable contact disengages the stationary contact, an arc box assembly is frequently provided which includes some means for producing a magnetic field directed laterally of the contact gap to produce a magnet deflecting force on the arc to drive the are up into the arc chamber stretching it out and causing the arc current to cease flowing in a relatively short period of time.

Arrangements for producing this arc interrupting field in the arc box chamber conventionally include a blowout coil which depends for its energization upon the contact current and are current, or a permanent magnet arrangement located in the arc box and having pole plates situated on opposite lateral sides of the contact assembly to produce a unidirectional magnetic field laterally of the contact gap to deflect the arc.

The blowout coil assembly has several disadvantages, one of the more important disadvantages being that the magnetic field produced thereby varies with the magnitude of the current inthe contact circuit. Secondly, such a coil is often one of the largest single sources of heating in the switch assembly, which can be very detrimental to switch operation and which may tend to shorten the life expectancy of the switch. Moreover, the coil arrangement, together with its pole plates for conducting the coil flux into the vicinity of the contact gap, represents a bulky construction requiring a relatively large arc box structure to house the complete assembly. These considerations coupled with the manufacturing costs due to the number of components and their relative complexity in assembly has indicated a need sometime for improvements which simplify the general configuration of the assembly.

The permanent magnet type offers certain advantages with respect to the blowout type of arc box structure, but this again is a relatively expensive construction because of the cost of the metallic permanent magnet employed to produce the magnetic field. In order to achieve the re quired degree of flux density, such a magnet is usually fairly large, occupying approximately the same space and approximately the same position as the blowout coil in the arc box assembly and, like the blowout coil, its magnetic flux is conducted to the region of the contact gap by means of pole plates forming a generally U-shaped as sembly in which the pole plates are each seated at one end'on opposite magnet pole faces of the metallic perman'ent magnet. Here again, the construction is relatively 2,875,304 Patented Feb. 24, 1959 expensive and bulky, posing roughly the same general electrical and thermal insulating problems that exist with the blowout coil type of arrangement but having the advantage of not producing heat in the arc box structure as does the blowout coil.

A further disadvantage of this permanent magnet type of assembly results from the stray field produced by the permanent magnet assembly. In view of the compact arrangement of such a relay, the electromagnetic actuating means is usually disposed in close proximity to the arc box assembly in which position the coil thereof is linked by the stray permanent magnet field. This field is strong enough to interfere with proper operation of the relay under certain conditions.

For instance, in an application wherein such a relay or circuit interrupter is utilized in controlling reciprocating movement of a planar platen, the voltage to the operating coil is reversed every time the table is reversed. This reverses. the main operating field which in itself has no effect on the operating characteristics of the relay. However, since the permanent magnet blowout field fiux is always in the same direction and this flux links the operating coil, the net operating flux for the arrangement varies with the direction of the main operating field. For one polarity of energization of the operating coil, the permanent magnet blowout flux aids the operating coil field flux. When this excitation or energization is reversed, then the permanent magnet blowout field opposes the operating coil field flux. The result is pick up, and drop out of the circuit interrupting devices are different for each direction of movement.

One object of this invention is to provide a circuit interrupting device in which. the pick up and drop out characteristics are essentially the same.

Another object of this invention is to provide a circuit interrupting device having an arc blowout assembly in which the stray magnet field is minimized so that interference with the operating coil field flux of the device is substantially obviated.

Yet another object of this invention is to provide a circuit interrupting device having an arc blowout assembly in which the magnet field strength diminishes with distance from the permanent magnet source at a rate which is higher than with conventional devices.

Still another object of this invention is to provide a circuit interrupting device having an arc blowout assembly producing a magnetic field of such character as to minimize the tendency for restriking of an are at the contacts during any one interruption cycle.

Further separate and combined objects of this invention are to provide a circuit interrupting device having an arc blowout assembly which is simple in construction with respect to operational requirements, which is cheaper and easier to manufacture than corresponding prior art devices as a result of simplification and the use of relatively inexpensive materials in its fabrication, and which is more compact for a given rating.

The foregoing statements are merely illustrative of the various aims and objects of this invention. Other objects and advantages will become apparent from a study of the following specification when considered in conjunction with the accompanying drawings in which:

Figure 1 is a front elevational view of a circuit interrupting device embodying the principles of this invention;

Fig. 2 is a side elevational view illustrated in Fig. 1;

Fig. 3 is a sectional view taken on line III-HI of Fig. 2;

of the arrangement Fig. 4 is a perspective view fragmentarily in section of the permanent yoke assembly of the arc box structure of the circuit interrupting device;

Figs. and 6 are respectively front and plan views of the magnet yoke assembly of this invention illustrating the magnet flux density at different distances from the approximate magnetic center of the arrangement;

Figs. 7 and 8 are respectively front and plan views of a magnet yoke assembly according to one prior art arrangement, and which is typical of prior art arrangements, illustrating the magnet flux density at different distances from the magnetic center of the assembly. This is provided for comparison with the inventive arrangement illustrated in Figs. 5 and 6;

Figs. 9 and respectively are front and plan views of the prior art arrangement shown in Figs. 7 and 8 illustrating therein the approximate pattern of the magnet field pattern associated with such an organization; and

Figs. 11 and 12 are respectively front and plan views of the permanent magnet yoke arrangement of this invention showing the approximate flux pattern associated therewith for the purposes of comparison with the flux pattern of prior art arrangement of Figs. 9 and 10.

The circuit interrupting device illustrated herein is disclosed in U. S. Patent 2,693,553 to B. C. Wells et al., and which is assigned to the assigriee of this invention. Thus, only such brief description of the general organization of this circuit interrupting device, as is deemed necessary to understand this invention, is given in this application. Further details relating to this device per se may be had by reference to the aforesaid patent. 7

Referring to Figs. 1 through 4, the circuit interrupting device illustrated, conventionallyidentified as a relay, is

mounted upon a main insulating back plate 1 which may be an insulating panel for receiving all such operational components of a control system. The relay assembly comprises a back plate 2 of magnetic material which is the main support member of the relay. At the upper end of this back plate an arc box structure generally designated 3 is mounted on guide members 4 and 5 which project outwardly from the back plate 2. Provisions are made, in part, through a slot 6 in guide member 5, through which a stud 7- mounted in the arc box assembly projects, to slidably move the arc box assembly toward and away from the back plate 2 to provide proper adjustment of the stationary contact assembly in the arc box with respect to the movable contact assembly. The arc box assembly is secured in any selected position in the range of adjustment by means of a thumb nut 8 which clamps the assembly against the guide member 5. Spaced confronting stationary contacts 9 and 10 are mounted in the front and rear portions respectively of an arc box chamber 11 formed internally of the arc box assembly 3. A movable contact assembly 12 is disposed in operating relation between the respective stationary contacts 9 and 10 to selectively engage these stationary contacts depending upon the control exerted thereon by an electromagnet actuating means generally designated 13.

The electromagnet actuating means is disposed beneath the arc box assembly as seen in each of Figs. 1 and 2. This assembly comprises a pair of laterally spaced cores 14 and 15 which are secured to the back plate 2 of magnetic material. Thus, a U-shaped magnetic core circuit is formed. Core 14 mounts a coil 16 and core 15 mounts a coil 17. 'Respective pole plates 18 and 19 are mounted on the ends of cores 14 and 15, and respective armature bearing pins 20 and 21 are secured adjacent the bottom ends of the respective pole plates 18 and 19, in positions projecting outwardly therefrom with the pin axes approximately paralleling the longitudinal axes of the cores.

An armature support plate 23 is provided with respective bearing edges 24 and 25 which ride in circumferential grooves in the respective bearing pins 20 and 21. This armature support plate mounts an armature plate 26 which straddles the lateral dimension across the respective pole plates 18 and 19 on the ends of the magnetic cores, and a movable contact arm 27 of electrical conducting material, which mounts the movable contacts at its free extremity, projects upwardly from the armature plate and supports the movable contacts 12 between the stationary contacts 9 and 10.

As described in the aforesaid patent, the circumferential grooves in the bearing pins 20 and 21 provide a convenient arrangement for adjusting the position of armature pivoting with respect to the core assembly, thereby providing a way of changing the calibration of the relay by changing the distance or gap between the armature plate 26 and the pole plates 18 and 19 on the ends of the magnet cores. However, such adjustment changes the relationship between the stationary and movable contacts Which is preferably maintained approximately as illustrated in Fig. 2. Thus, the provision of a slidably mounted arc box provides a way for sliding the arc box and stationary contact assembly to positions corresponding to the position of the armature pivot thereby maintaining this relationship between the stationary and moving contacts so that efiicient contact operation and relatively consistent striking of arcs at contact separation is maintained which is an important factor in arc extinguishing problems.

The details of the arc box assembly will be particularly understood by reference to Figs. 3 and 4. The are box assembly may be of a single piece molded configuration as shown, usually being molded from some form of heat resistant electrical insulating material. This are box, which is provided'with the arc chamber 11, comprises side walls 28 and 29 which define the arc chamber. This arc box is provided with an opening through its bottom through which the movable contact arm 27 projects and is provided further with suitable arc chutes 30 and 31 as seen in Fig. 2 through its upper surface to provide for the venting of gases and heat from the arc chamber. 7

This arc box assembly is supported in a U-shaped yoke 32 of magnetic material, which may be cold rolled steel, and which is provided with substantially parallel side members 33 and 34 which straddle the side walls 28 and 29 of the arc box structure. Respective ceramic permanent magnets 35 and 36 are disposed between the respective side members 33 and 34 and' the associated arc box sides 28 and 29, as seen in Fig. 3. As will be seen with reference to Fig. 4, these ceramic permanent magnets are essentially of the form of thin plates in which the large face surfaces in each are the north and south pole faces of the magnets. The confronting pole faces, disposed adjacent the opposite sides of the arc box structure, are of opposite polarity. The particular polarity need not be as shown, since this depends upon the direction of the arc current flow and is usually selected so that the arc which is drawn between the separating contacts will be blown upwardly due to the force resulting from the interaction of arc magnet field and permanent magnet blowout field. The outer or remote pole faces of these ceramic permanent magnets engage the inner confronting faces of the parallel legs of the U-shaped yoke. Thus, a flux path between these other pole faces is provided through the magnetic conducting material of the yoke which tends to minimize the stray field and which also prevents field reversal, as will be explained at a later point.

The parallel legs 33 and 34 of the magnet yoke 32 are slidably mounted in suitable slots 37 and 38 which extend longitudinally of the guide members 4 and 5. The threaded stud 7, which is secured against rotation in the leg 34 of the yoke 32, projects through slot 6 in guide member 5 and, as previously described, is secured by the thumb nut 8 in any selected position longitudinally of the guide members.

For assembly purposes, to prevent unwanted displacement of the permanent magnets 35 and 36 with respect to the parallel legs of the yoke which they engage, re-

l spective pins and; 40 and punchings 41 and 42 are provided in the respective legs in positions to be received by notches 43 cut in the ends of the magnets. The magnet pull, or attraction of the magnetic field of each magnet, seats the magnets securely against the respective parallel legs, and sliding movement to any extent in any direction is prevented by means of interlocking of the notches with the pins and punchings.

The are box structure 3 is secured to the bight section of the magnetic yoke. To this end, suitable holes are provided in the rear face of the arc box structure to receive locating dowels 44, which project from the bight section of the yoke, and the arc box is secured to a vertical extension of the bight section 45 by means of a screw 46 passing through the rear wall of the arc box structure and threading into a threaded hole in the vertical extension 'of the bight section.

Referring now to Figs. 5 and 6, respectively illustrating front and plan views of the magnets of this invention and Figs. 7 and 8, respectively showing front and plan views of a conventional magnet yoke assembly, typical flux densities for the two arrangmeents are indicated. These flux densities, at different distances from the magnetic center of the respective assemblies, were determined by magnet field detecting probes, the approximate positions of which are generally indicated at 49 in the respective figures. Movement of these probes in equal increments of distance as indicated by the arrows, was made, in each case, in order to determine the flux density at a particular distance from the magnetic center of the magnetic assembly. As will be seen by referring to Figs. 5 and 7, the numerical values of the flux density in gausses indicates a higher flux density at the magnetic center of the assembly of Fig. 5 with respect to that of Fig. 7 and further indicates a higher rate of magnet flux reduction between corresponding distances from the magnetic centers of the respective devices. For example, in Fig. 5, the flux density is 8 gausses at a distance corresponding to that in Fig. 7 at which a fiux density of 30 gausses is indicated.

This rapidly diminishing flux density has two advantages. First, the strength of the stray magnetic field diminishes to such an extent with distance that flux linkage of this stray field with the electromagnetic assembly of the relay does not interfere with the pick-up and dropout characteristics of the relay. With an arrangement such as shown in Fig. 7, however, the stray field linking the electromagnetic operating assembly is sufficiently strong to result in marked differences between the pickup and drop-out characteristics of the relay. Additionally, the rapidly diminishing magnetic field produced by the arrangement of the present invention minimizes the tendency for premature extinction of the are due to excessive arc stretching in the early periods of contact separation. With an arrangement such as shown in Figs. 7 and 8, the high density of the magnetic field existing at a substantial distance from the magnetic center of the assembly, results in extremely rapid arc deflection over undesirably large distances. As a consequence the arc is usually extinguished while the contacts are closely spaced during the opening cycle, and the circuit voltage is yet sufficiently high to cause re-striking of the arc. Thus, the general assembly illustrated in Figs.'5 and 6 provides a more desirable distribution of flux density maintaining a fairly high flux density in the region in which the arc is struck while providing a sufficiently weak field with increasing distances so that excessive arc deflection does not result.

Figs. 9 and 10 show a typical theoretical configuration of the magnetic field of a conventional permanent magnet yoke arrangement, and Figs. 11 and 12 show the general theoretical configuration of the magnetic field associated with the magnetic yoke arrangement of this invention. These are merely shown for the purposes of better illustrating and explaining the improvement afforded by the present invention and are not to be construed as limiting configurations with regard to actual specific-conditions. ;The problem here is merely that of illustrating that the magnetic field associated with Figs. 11 and 12 involves less stray flux than that associated with Figs. 9 and 10, in view of the flux path provided by the yoke connecting the outer pole faces of the permanent magnets. It will be noted from this that the flux distribution is substantially different from the conventional U-shaped or horse-shoe type of magnetic yoke arrangement which is typical of the prior art assembly.

The ceramic permanent magnets herein referred to are generally in a class of electrical insulating permanent magnets preferably formed of a magnetized non-metallic permanent magnet material. Such a material may be a ceramic permanent magnet material selected from the group: BaO-6Fe O (which also may be written BaFe O and SHO'6FGZO3.

This material is made by reacting, at high temperatures, solid oxides in the proper proportions, and it produces a ceramic-like material which is hard and reasonably strong and is shaped mainly by pressing it in the desired shape before firing. After firing, sizing to the desired dimensions may be accomplished by grinding. This material has desirable magnetic properties. Both coercive force, H and the intrinsic coercive forces are unusually high for commercial permanent magnet material. The demagnetization characteristics of the material indicate a high order of stability.

Another important property of such materials which is particularly advantageous in these applications is their high electrical resistance. For instance, the material BaO-Fe O has an electrical resistance of the order of 10 ohms/omi Since the material is self-insulating, it need not be insulated from other parts of the switch. This permanent magnet material can also be readily coated with a vitreous enamel, fired again and then magnetized. This finish provides still more resistance to arcing.

The use of the yoke 32 of magnetic material has several advantages. First, this magnetic yoke, by providing a flux path between the outer or remote faces of the respective permanent magnets, prevents a reversal of the magnetic field as the field extends outwardly from the magnet center. The magnetic field is of one polarity between the inner pole faces and of reversed polarity between the outer pole faces. However, by utilizing yoke 32 to shunt the outer pole faces, the field due to the outer pole faces is confined almost entirely to the magnetizable yoke. As a consequence, the arc deflecting field is unidirectional, and the stray outer magnet pole field is essentially a weak local field in and about the magnetic yoke. Thus, a reversal in field, which would normally stop the arc at the point of reversal, is obviated. The yoke not only provides a means of obtaining a properly shaped field but also strengthens the field at the contact by over 50%. This has been confirmed by tests made with correspondingly spaced magnets, one set of which was shunted by the magnetizable yoke and the other set of which was not. As a typical example, the magnetic field detected with one pair of shunted magnets, at the magnetic center of the magnets, had a strength of about 350 gausses, whereas with the same pair of magnets in correspondingly spaced relation, but without the magnetizable yoke, the field strength amounted to about 225 gausses at the magnetic center. The outer pole leakage flux strength is considerably less when the magnetic yoke shunts the outer pole faces of the ceramic permanent magnets. The leakage flux density at the center is only about 12 gausses, whereas with the unshunted assembly the leakage flux strength ranges as high as gausses in the same location.

From the foregoing considerations, it will be appreciated that a circuit interrupting device has been provided herein having marked improvements over prior art devices not only from the standpoint of economies '2 realized in structural simplicity and reduction of cost of materials, but also from the viewpoint of operation, wherein improved configurations of the magnetic fields used for are interrupting purposes have been obtained Although but one embodiment of this invention has been herein illustrated and described, it will be appreciated by those skilled in the art that variations of this invention both in its details and in the organization of such details may be made without departing from the spirit and scope hereof. Accordingly, it is intended that the foregoing disclosure and the showings made in the drawings shall be considered only as illustrative of the principles of this invention and not construed in a limiting sense.

I claim as my invention:

1. A circuit interrupting device comprising, a contact assembly having stationary contact means and movable contact means operable to engage and disengage said stationary contact means; a permanent magnet blowout assembly disposed adjacent said contact means and producing a magnetic field directed substantially laterally of said contact means, said permanent magnet blowout assembly including a yoke having a pair of spaced parallel members of magnetic material disposed on opposite lateral sides of said contact assembly and a pair of electrical insulating permanent magnet members respectively disposed against the confronting faces of said spaced parallel members and poled in aiding magnetic relation.

2. A circuit interrupting device comprising a contact assembly having stationary contact means and movable contact means operable to engage and disengage said stationary contact means; a pair of electrical insulating permanent magnetic plates magnetized so that the respective large faces thereof are the north and south magnetic poles, said electrical insulating permanent magnet plates being disposed on opposite lateral sides of said contact assembly with a north pole face confronting a south pole face, and a yoke member of magnetic material having a pair of spaced parallel legs the respective inner faces of which engage the respectiveouter faces of said electrical insulating permanent magnets and providing a flux path between'the outer magnet pole faces.

3.'A circuit interrupting device comprising, support means, a yoke of magnetic material having spaced parallel sides, an arc box having an arc chamber therein, means mounting said are box on said yoke member between said spaced parallel sides, means mounting said yoke member on said support, a pair of electrical insulating permanent magnets respectively disposed between the respective parallel sides of said yoke and the confronting side of said are box and poled in series magnetic'aiding relationtto produce a magnetic field across said are chamber, stationary contact means disposed in said are chamber, movable contact means disposed in operable relation with respect to said stationary contact means, and means operably associated with said movable contact means to effect movement thereof between positions engaging and disengaging said stationary contact means.

4. Apparatus of the character set forth in claim 3 wherein said last-named means comprises a movable armature member connected with said movable contact means, and electromagnetic means mounted on said support and producing a magnetic field when energized which operably links said armature member.

5. A circuit interrupting device comprising support means, a yoke of magnetic material having spaced parallel sides, an arc box of electrical insulating heat resistant material having an arc chamber therein, means mounting said are box on said yoke member between said spaced parallel sides of said yoke member, a pair of guide members projecting from said support in laterally spaced substantially parallel relation and respectively slidably receiving said parallel sides of said yoke member affording sliding movement of said are box and yoke member toward and away from said support, a pair of electrical insulating permanent magnets respectively disposed between the confronting faces of said are box and the respective parallel sides of said yoke member and poled in series aiding magnetic relation to produce a magnetic field across said are chamber, a stationary contact disposed in said are chamber, a core projecting from said support means, a coil on said core, a movable armature, an adjustable pivot means selectively pivotally mounting said armature for pivotal movement at different distances from the end of said core, said arc box and yoke being adjustable along said guide members in correspondence with the positioning of said adjustable pivot means.

6. In an arc box assembly, an arc box of electrical insulating material having an arc chamber therein, 'a substantially U-shaped member of magnetic material having spaced substantially parallel legs, a pair of electrical insulating permanent magnets respectively mounted on the inner faces of said legs adjacent the extremities thereof, and poled in series aiding magnetic relation producing a unidirectional magnetic field therebetween, the magnetic field between the outer pole faces of said electrical insulating permanent magnets being confined substantially to said U-shaped member, and means relatively supporting said are box and said U-shaped member with said electrical insulating permanent magnets disposed at opposite sides of said are chamber with said magnetic field directed laterally of said are chamber.

7. In an arc box assembly, an arc box of electrical insulating material having an arc chamber therein, a substantially U-shaped member of magnetic material having spaced substantially parallel legs, a pair of electrical insulating permanent magnets respectively mounted on the inner faces of said legs adjacent the extremities thereof, and poled in series aiding magnetic relation producing a unidirectional magnetic field therebetween, the magnetic field between the outer pole faces of said electrical insulating permanent magnets being confined substantially to said U-shaped member, and means relatively supporting said are box and said U-shaped member with said electrical insulating permanent magnets disposed externally of said are box with said magnetic field directed laterally of said are box and are chamber.

References Cited in the file of this patent UNITED STATES PATENTS 

